<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>效率测试</title>
</head>

<body>
</body>
<script>
    function fn() {
        var d1 = +new Date();

        var str = '';
        for (var i = 0; i < 1000; i++) {
            document.body.innerHTML += '<div style="width:100px; height:2px; border:1px solid blue;"></div>';
        }
        var d2 = +new Date();
        console.log(d2 - d1);
    }
    fn();
</script>

</html>